A phenol-based compartmental ligand as a potential chemosensor for zinc(ii) cations

An "end-off"-type compartmental Lewis base, 2,6-bis(2-hydroxybenzyl-2-hydroxyethylamino)methyl-4-methylphenol (L), was synthesized as a potential chemosensor for Zn2+ ions. L coordinates two Zn2+ cations in methanol-water solution, forming a dinuclear complex whose formulation was confirmed by ESI-MS spectroscopy and Job's plot. The fluorescence of L is remarkably enhanced by Zn2+ as compared with K+, Ca2+, Mg2+, Cu2+, Pb2+, Mn2+, Fe3+, Fe2+, Co2+, Cd2+ and Ni2+ ions. The fluorescence enhancement is attributed to the complexation of Zn2+ with L, which interrupts the photoinduced electron transfer process and rigidifies the molecular skeleton of L. The fluorescence of L is greatly dependent on the acidity and polarity of the solvents. This compound may be used as a probe to sense Zn2+ ion in polar protic solvents after proper modification

Catalytic enantioselective synthesis of alpha-amino acids and alpha,alpha-dialkyl amino acids by phase-transfer catalysis. (Volumes I and II)

A new method for a catalytic asymmetric synthesis of $\alpha$-amino acids using phase-transfer catalysis has been developed. The methodology developed to date allows preparation of either enantiomer of a variety of types of target amino acids in up to 66% ee by a simple and straightforward procedure at room temperature from readily available starting materials. The ability to scale the reaction up and the possibility of preparing $\alpha$-amino acids in high optical purity have been demonstrated by synthesis of 6.5 g of 4-chloro-D-phenylalanine in $\u3e$99% ee from 19.2 g of starting substrate. This has resulted the first practical asymmetrical synthesis of $\alpha$-amino acids using phase-transfer catalysis. This method has been extended to the preparation of $\alpha$,$\alpha$-dialkyl amino acids from the starting material aldimine ester by solid-liquid phase-transfer catalysis. The alkylation of aldimine ester with less active alkyl halides in up to 70% ee has been successfully carried out under the condition of high concentration of substrate or in the absence of organic solvent. A mild, safe and economical method has been developed for the synthesis of various novel chiral phase-transfer catalysts. Alternative approaches to preparation of either O-alkyl N-alkyl or O-alkyl N-benzyl as well as dimer cinchona quaternary catalysts were developed. Most of these novel catalysts have shown good optical induction (up to 70% ee) in the alkylation reaction. A key finding is the first direct evidence for the O-alkyl N-benzyl cinchona quaternary catalysts as the active chiral phase-transfer catalyst in our alkylation system. The discovery of this result is inconsistent with the current mechanistic concept of chiral phase-transfer catalysis. Additionally, systematic studies of the pathways of formation of racemic products, the nature of the catalyst in the reaction process and the isolation and identification of the various by-products formed from the reaction process has resulted in a new mechanistic proposal for the reaction

Superior fracture toughness with high yield strength in a high-Mn steel induced by heterogeneous grain structure

Heterogeneous grain structures were designed in a high Mn steel (Fe28Mn10Al1.00C), and the tensile properties and fracture toughness were investigated and compared with those for homogeneous structures. The heterogeneous grain structures display larger tensile ductility, stronger strain hardening and higher fracture toughness at the similar yield strength level. Hetero-deformation-induced hardening is found to play an important role in the heterogeneous grain structures, resulting in better mechanical properties. The size of plastic zone and the strain hardening capacity around the crack tip for the heterogeneous grain structures are found to be much larger/higher than those for the homogeneous grain structures at the same level of yield strength, resulting in better fracture toughness. High density of geometrically necessary dislocations and grain refinement are induced at the adjacent area of the main crack path, and numerous microvoids are also observed besides the main crack for the heterogeneous grain structures, resulting in more energy dissipation for higher fracture toughness. The deformation mechanisms around the crack tip are highly dependent on the magnitude of plastic strain and the grain size. The observed higher fracture toughness in the heterogeneous grain structures can be partly attributed to the formation of microbands. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

The role of glycine in the ammonium thiocyanate leaching of gold

Thiocyanate leaching is an efficient and environmentally friendly method to extract gold due to fast leaching speed, excellent reaction selectivity and slight environmental risks, but thiocyanate is easily oxidized to decompose by oxidant in the leaching process, resulting in large consumption of leaching agent. In this work, synergistic leaching experiments were carried out with a mixed reagent system of ammonium thiocyanate and glycine for exploring the role of glycine in thiocyanate leaching. And the theoretical mechanism of glycine in thiocyanate leaching was also investigated. The results showed that as glycine was added into the thiocyanate leaching solution, the decomposition reaction of thiocyanate would be lessened, resulting in lower ammonium thiocyanate consumption. Meanwhile, owing to its characteristic of gold dissolution, glycine can be used as an additional leaching agent to increase the gold leaching ratio. Optimized gold-extraction efficiency (93.15%) of gold-bearing flotation concentrate was achieved under the following conditions: a concentration of thiocyanate, glycine and oxidant Fe3+ at 0.6 mol/dm(3), 5 g/dm(3) and 0.05 mol/dm(3), respectively; stirring speed at 600 rpm; pH at 2; temperature at 298 K; leaching time of 3 h and a liquid-solid ratio of 4:1

Extraordinary fracture toughness in nickel induced by heterogeneous grain structure

The tensile properties and fracture toughness of both heterogeneous grain structures and homogeneous structures in pure nickel have been investigated and compared. The heterogeneous samples were found to show much larger uniform elongation and much higher fracture toughness at the similar level of yield strength, compared to the homogeneous structures. The enhanced ductility/toughness can be attributed to the stronger heterodeformation-induced hardening for the heterogeneous structures. In sharp contrast to the cleavage-like and brittle fracture behavior in the homogeneous hot-extruded and cold-rolled samples, the fracture process in the heterogeneous structures shows ductile fracture by microvoid coalescence and dimples. The crack path in the heterogeneous structures was found to display a gourd shape, which can result in longer crack length and dissipate more energy for better fracture toughness. Hardening is obvious across a much larger area around the crack tip in the heterogeneous structures as compared to the homogeneous structures, indicating a much larger plastic zone for the heterogeneous structures. The strong strain hardening at the crack tip was found to be induced by the grain refinement of the coarse grains in the heterogeneous structures, resulting in extraordinary fracture toughness

Basic theory and optimization of gold containing antimony concentrate leaching by alkaline sulfide

As sodium sulfide is easily oxidized to polysulfide and thiosulfate which have a gold leaching effect, gold would dissolve in leaching solution when extracting stibium from gold containing antimony concentrate by alkaline sulfide. Through leaching test and kinetics analysis, the decomposition regularity of sodium sulfide and leaching rate were studied under different leaching conditions. The results indicated that the gold content in antimony concentrate was 28.41g/Mg, and the content of antimony and sulfur was 36.01% and 14.04%, respectively. The main metallic minerals were native gold, arsenopyrite, stibnite, and the gangue minerals were mainly quartz. Anodic polarization curve shows reduced iron powder can increase the peak potential of the oxidation of the leaching solution and it can effectively prevent the decomposition of sodium sulfide and the dissolution of gold. Optimized stibium-extraction efficiency was achieved under the following conditions: a concentration of sodium sulfide and sodium hydroxide at 110g/ dm(3) and 20g/dm(3), respectively; a ratio of iron powder to concentrate of 1:30; a ratio of liquid to solid of 5:1; agitation speed of 600rad/min; reaction temperature of 353.15K; and a reaction time of 3 h. Under the optimized conditions, high antimony recovery (97.35%) and low gold dissolution (1.32%) were achieved.</p

Excellent dynamic properties and corresponding deformation mechanisms in a microband-induced plasticity steel with dual-heterogeneous structure

A dual-heterogeneous structure with dual phases and heterogeneous grains was designed in a high Mn microband-induced-plasticity (MBIP) steel. The heterogeneous structured sample exhibits similar dynamic shear yield strength, while exhibiting enhanced dynamic uniform shear strain and dynamic shear toughness by 36 % and 47 %, respectively, as compared to the homogeneous structured sample. The strain hardening mechanisms contributing to the excellent dynamic shear properties in the heterogeneous structured sample have been revealed. Firstly, the superior hetero-deformation-induced hardening capability of the heterogeneous structured sample arises from a higher density of geometrically necessary dislocations induced in each phase. Secondly, a pronounced strain rate effect is observed in body-centered cubic (BCC) grains and face-centered cubic (FCC) ultra-fine grains, leading to an elevated level of strain rate sensitivity. Finally, the MBIP effect is also observed in FCC coarse grains under dynamic loading. Moreover, the MBIP effect in FCC ultra-fine grains is more likely to occur at high strain rates due to the emergence of single-wall domain boundaries, which is not observed during quasi-static tensile testing. The present results provide new routes for designing impact-tolerant structures in advanced metals and alloys